The epidemic of marijuana use disorders among young people mandates research to develop novel approaches to prevention and treatment. Emotional states and social contexts are associated with desire to use marijuana, suggesting that interventions may be more effective if administered in real life, as triggers for use are bein experienced. This study proposes a pilot randomized trial to further develop and test the Momentary Self-Monitoring and Feedback + Motivational Enhancement Therapy (MOMENT) intervention, a real-time, contextual intervention to reduce marijuana use among primary care patients. The MOMENT intervention provides state-of-the-art motivational enhancement therapy (MET) in two brief office-based sessions, then uses a mobile device to prompt report of in-the-moment affective states, social context, marijuana desire and recent use in response to signals 4-6 random times/day for two weeks. Based on report of affective and social triggers for use, desire for marijuana, and use-related behaviors, the mobile device provides messages designed to build on the MET by supporting self-efficacy and prompting participants to consider their individualized coping strategies. Individuals also use the mobile device to complete daily diary reports summarizing use and motivation to reduce use. The specific aims of this study are to evaluate the feasibility and preliminarily test the efficacy of the MOMENT intervention to reduce momentary marijuana desire when in triggering contexts and to reduce marijuana use following exposure to triggers and to reduce overall frequency of use, dose per use, and motivation to reduce use. To determine the relative contributions of the three components of this intervention, youth 15-24 years attending two primary care clinics who use marijuana at least three times/week (N=108) will be randomized to one of three arms: 1) the full MOMENT intervention, 2) MET + momentary and daily self-monitoring, but no feedback, or 3) MET only. Rates of response to assessments and retention will be determined and exit interviews will assess acceptability, usability, and burden. At baseline and three months, participants will complete questionnaires in a visit and momentary and daily assessments over one week. The results will be compared to determine the effect of the intervention on the marijuana-related outcomes and be used to estimate effect sizes for an R01 application to conduct a larger, longer-term randomized trial.